Thymopoietin is a thymic hormone that selectively induces differentialtion of prothymocytes to thymocytes. Thymopoietin pentapeptide (TP-5), a synthetic pentapeptide corresponding to amino acids 32-36 of the 49 amino acid thymopoietin polypeptide chain, has been shown to have similar biologic activity to thymopoietin itself. In vitro inclubation of human leukocytes with TP-5 has been reported to increase the number of E-rosette forming cells, to increase proliferative responses to mitogens, and to increase phagocytic acitivity of polymorphonulear leukocytes. Preliminary trials of TP-5 in man have produced no demonstrable toxicity, and evidence has been obtained that depressed numbers of E-rosette forming cells and phagocytic activity of neutrophils may be enhanced after in vivo administration. In this Phase I study we propse to evaluate the effects of TP-5 on cellular and humoral immunity in patients with Hodgkin's disease and epidermoid cancer of the head and neck who show evidence for immunodeficiency. Our selection of these patient groups is based on the observation that such patients often show abnormal cell-mediated immune reactions, even in untreated patients with limited extent of disease. Both escalating and chronic dose schedules of TP-5 will be used in an attempt to define the optimal dose and schedule of TP-5 administration, to observe any untoward side effects, and to seek evidence for therapeutic efficacy. We will focus our attention on a limited number of studies to evaluate T-cell differentiation markers (total and active E-rosettes; IgG and IgM receptors on T cells; terminal deoxynucleotidyl transferase activity in peripheral blood and bone marrow) and T-cell function (proliferative responses to mitogens, antigens and allogeneic cells; helper and suppressor function in terms of B-cell differentiation in polyclonal and antigen-dependent plaque assays), and will applQ several methods for measurement of thymic hormone activity in the serum.